Abstract
Despite countless recent advances in fracturing fluids, traditional borate crosslinked guar fluids persist as a preferred fluid for hydraulic fracturing. The advantages of borate gels are numerous and include superior proppant carrying capability in difficult to fracture reservoirs, as well as high stability in high temperature and high shear conditions. However, borate fluids are not without notable disadvantages. The most obvious disadvantage is the presence of insoluble polymer residue that remains in the proppant pack after the gel has been broken with oxidizer breakers. Oxidizing breakers cleave the polymer chains at random sites resulting in a mixture of residual fragments which may remain crosslinked. These residual polymer fragments have been shown to significantly impair the proppant pack conductivity. Further compounding this problem, any residual unbroken gel at a high pH is susceptible to re-crosslinking when exposed to multivalent ions such as iron or calcium from the wellbore or formation.
Through the addition of a novel in-situ self-generating acid in combination with an oxidizing breaker, the degradation of borate crosslinked guar is notably improved. The controlled release of an acid, which is uniformly distributed throughout the gel, will lower the pH of the fluid thereby completely removing the crosslink from gel polymer fragments. This lower pH will result in an increase in solubility of the residue, improving clean-up of a proppant pack.
It has been shown that the addition of the self generating acid dramatically improves the regain conductivity of the proppant pack. Additionally the lowered pH of the fracturing fluid aids in the prevention of re-gelling upon flowback, reduces the water reactivity with water sensitive clay minerals, and aids in the removal of polymer residue from the well after treatment. Each of the mentioned benefits will aid in allowing the reservoir and conductive path to reach its full production potential.
